The use of X-rays in medical diagnosis presently is widespread.
According to conventional techniques, an image is recorded by a radiographic film, squeezed between intensifying screens in a cassette. After exposure, the radiographic film is taken out of the cassette in a darkroom or the cassette is loaded in full daylight in a film handling and processing equipment such as the apparatus marketed by Agfa-Gevaert N. V., Belgium under the trade name CURIX CAPACITY PLUS, and the film is then processed in a photographic processor to yield the final radiographic image suited for medical diagnostic purposes.
Particulars of the overall radiographic process may be found in `Medical X-Ray Technique, principles and applications` by G. J. Van der Plaats, Philips' Technical Library, 1959, `Radiographic Processing in Medicine and industry` by D. H. O. John, The Focal Press, 1967, `The Fundamentals of Radiography`, publication by the Health Sciences Markets Division, Eastman Kodak Company, 1980, or numerous other publications in the field.
The conventional way of producing a radiographic image on film offers however some disadvantages, in particular in respect of archiving and retrieving the images.
Numerous radiological examining procedures already directly yield images suitable for diagnostic evaluation in digital form. Examples include digital subtraction angiography, magnetic resonance imaging, digital projection radiography using stimulable phosphor plates and computer tomography.
A general overview of e.g. the digital image radiographic system is set forth in the article from Minoru Gonoda et al, in "Radiology", September 1983, p. 833: "computed Radiography utilizing Scanning Laser Stimulated Luminescence".
However as long as radiographic techniques that yield directly images in digital form remain expensive, the classical filmradiography will keep its place within the diagnostic department of a hospital. On the other hand the need to have the radiographic image (diagnostic information and patient data) available in digitized form grows mainly for two reasons. First a digital image may be processed in any of the various ways offered by digital image processing apparatus, which enhances the diagnostic possibilities. Secondly such an image in digital form may enter into the digital information flow of the hospital.
It is thus of utmost importance that the conventionally produced films can be entered not only into the digital image processing environment but also into the digital information system of the hospital.
The technique for digitizing images is well known, e.g U.S. Pat. No. 4,442,453 and many devices to perform digitization of film are commercially available.
Apparatus particularly dedicated for the digitization of radiographic images are commercially available under the trade names `TRUSCAN` from Truvel Corp., 8943 Fullbright Avenue, Chatsworth, Calif. 91311, USA, `300A Computing Densitometer` from Molecular Dynamics, 240 Santa Ana Court, Sunnyvale, Calif. 94086, USA, `Laser Scanner KFDR-S` from Konica Corp., Medical Products Marketing Division, Shinjuku Nomura Building No. 26-2, Nishishinjuku 1-chome, Shinjuku-ku, Tokyo 163, Japan, e.a.
Now the digitization of conventionally produced films proceeds as follows: the exposed and processed radiographic films are retrieved out of the archives, then they are placed on a film digitizing apparatus, the operating conditions of which are adjusted to take into account the particulars of the radiograph, such as format, desired resolution etc. and after digitization the digitized image is sent to a host computer by the digitizer, and the radiographic film is set again in the archives.
Working off-line, i.e. digitizing after the total processing, the first diagnosis and archival of the films, is a cumbersome and significantly labour-intensive procedure. A method for digitizing film during the processing has been proposed in U.S. Pat. No. 5,101,286 in connection with amateur and professional films.
In X-ray radiography the need for digitized images arises mainly in these hospitals that use a high volume of X-ray films. In advanced equiment for handling conventional X-ray film, e.g. the daylight filmhandling center marketed by Agfa-Gevaert N. V., Belgium under the trade name of CURIX CAPACITY PLUS, the access-time of the film is kept very low. The CURIX CAPACITY PLUS daylight filmhandling center in conjunction with the photographic processor marketed by Agfa-Gevaert N. V., Belgium under the trade mark CURIX HT 530 makes the image on film available for diagnosis within 1 minute. The transport speed of the film through the processor is accordingly high and is set in the range of 200 cm/min to 290 cm/min.
Although the need for digitizing is high in those high volume hospitals, the need for rapid access to the information is even higher. This means that a digitizer for use in an X-ray department on-line with a high capacity processing machine has to be so fast working as not to extend the access-time to the radiographic image.
In radiography the film-size that will be used depends largely on the examination at hand, in a typical radiography department the film-sizes used may vary from 5".times.7" to 14".times.17", and the digitizer has to accomodate all sizes.